At the present time, there are active or passive optical devices, for example, coupling structures, waveguides, modulators and photodetectors, that may be integrated into photonic integrated circuits.
Moreover, another known advantageous component is a hybrid III-V/Si laser source. Such a laser source comprises a gain medium including a III-V composite semiconductor, a waveguide located in a subjacent silicon layer and optically coupled to the gain medium and a resonant cavity optically coupled to the waveguide and, for example, comprising Bragg mirrors. The gain medium, when it is excited (pumped) with electrical power, emits light, and the resonant cavity is intended, via interaction with the gain medium, to amplify this light so as to deliver the laser beam.
Depending on the type of laser (DBR (distributed Bragg reflector) laser or DFB (distributed feedback) laser), the Bragg mirrors are located in the silicon on the periphery of the gain medium or under the gain medium.
Such a hybrid laser source may require the distance between the gain medium and the subjacent “waveguide/resonant cavity” assembly, which is made of silicon, to be very small, typically no more than about one hundred nanometers. Moreover, the molecular bonding of the gain medium to such an assembly of the silicon-on-insulator type may require a flat surface prepared by a step of chemical-mechanical polishing.
At the present time it is known how to produce an individual III-V hybrid laser source on a silicon substrate in the laboratory.
Moreover, a photonic integrated circuit integrating a hybrid III-V on silicon (III-V/Si) laser source is described in a French patent application published under the number 3,007,589. Conventionally, for photonic integrated circuits intended for wavelengths ranging from 1310 nm to 1550 nm, it may be preferable to have a silicon layer that is not too thick, typically smaller than or equal to 300 nm in thickness, in order not to compromise the operational effectiveness of the silicon photonic components contained therein, whereas a thicker silicon layer, typically 500 nm in thickness, is necessary to form, facing the III-V/Si hybrid laser, a waveguide optically coupled to the latter, in order to pass light effectively from the resonant cavity of the laser to a silicon photonic component.
Provision is thus made to place the gain medium of the laser source on an additional thickness of silicon. This additional thickness may be a layer of amorphous silicon separated from the subjacent silicon layer (especially containing the other photonic components) by a layer of silicon dioxide.
However, amorphous silicon is a relatively unstable material and this may lead to degradation of the reliability and performance of the laser source. Moreover, it is difficult to form an amorphous silicon layer of uniform thickness on the scale of an entire wafer.
Furthermore, it is not easy to integrate the use of amorphous silicon into the steps currently used in CMOS fabrication processes.